Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation. Supercoiled strands remain after replication, which is never completed.

Verified step by step guidance

1. Identify the normal process of DNA replication in E. coli, focusing on the role of enzymes involved in unwinding and relieving supercoiling.
2. Understand that during DNA replication, the DNA must be unwound and supercoiling must be relieved to allow the replication machinery to access the DNA strands.
3. Recognize that topoisomerases are enzymes responsible for relieving supercoiling by cutting the DNA strands, allowing them to rotate and relieve tension, and then rejoining the strands.
4. Consider that if supercoiled strands remain after replication, it suggests a malfunction in the enzyme responsible for relieving supercoiling, likely a topoisomerase.
5. Predict that the mutation affects the function of a topoisomerase enzyme, preventing it from relieving supercoiling, which in turn hinders the completion of DNA replication.

Key Concepts

DNA Supercoiling

DNA supercoiling refers to the over- or under-winding of the DNA double helix, which is crucial for DNA replication and transcription. In prokaryotes like E. coli, supercoiling helps compact the DNA and maintain its structure. If supercoiled strands remain after replication, it indicates that the DNA is not being properly unwound and separated, which can hinder the completion of replication.

Topoisomerases

Topoisomerases are enzymes that manage DNA supercoiling by introducing or removing twists in the DNA strands. They play a critical role during DNA replication by relieving the tension that builds up ahead of the replication fork. Mutations affecting topoisomerases can lead to incomplete replication, as the DNA cannot be properly unwound, resulting in supercoiled strands.

Temperature-Sensitive Mutations

Temperature-sensitive mutations are genetic alterations that result in a protein being functional at one temperature but non-functional at another. In the context of E. coli, these mutations can affect enzymes involved in DNA replication, such as topoisomerases. At non-permissive temperatures, the affected enzyme may fail to function, leading to issues like incomplete replication and the accumulation of supercoiled DNA.